(1) Field of the Invention
This invention relates to a thermal printer of heat-sensitive type or thermal transfer-printing type.
(2) Description of the Prior Art
Generally, in thermal printers of the prior art, a thermal head has been moved along a line of printed characters while pressing against a printing sheet, and a multiplicity of heat generating elements located in the thermal head have been selectively actuated to generate heat to perform printing. When a printing operation is finished or when it is interrupted, the thermal head has been urged by means of a solenoid or a resilient member to move to a position in which it presses against the printing sheet or a position in which it is released from pressing engagement with the printing sheet. In the thermal printer of the type which uses a resilient member to bring the thermal head into pressing engagement with the printing sheet by its biasing force, a problem has been raised with regard to operability. More specifically, even if a switch is actuated to turn off the power source, the thermal head is still maintained in pressing engagement with the printing sheet, so that a head release level should be actuated to move the thermal head away from the printing sheet when it is desired to remove the printing sheet and set a new printing sheet or to replace the thermal transfer-printing ribbon by a new one. Particularly when the thermal printer is of a thermal transfer-printing type, the thermal transfer-printing ribbon might be pulled excessively when the printing sheet is pulled manually while the power source is an OFF condition, thereby inadvertently damaging the thermal transfer-printing ribbon. When the thermal printer is of a type in which a solenoid is relied on to bring the thermal head into and out of pressing engagement with the printing sheet, it is necessary to maintain the solenoid in an energized condition. This has given rise to the problem that power consumption is high. Particularly when the thermal printer relies on a battery as a source of motive power, the battery used has a short service life.